Generally, total inner reflection Fresnel (TIRF) lenses are compact and efficient collimators. To provide a lighting device with a higher intensity and/or a more robust construction, it is desirable to use an extended light source in combination with such TIRF lenses. However, standard TIRF-lenses are optimized for point-like sources. When utilizing an extended light source, normal designs are unable to control all light. This leads to light leakage which in turn results in a reduction of efficiency and beam intensity.
Thus, there is a need for improvement of a TIRF-lens for directing light from an extended light source.
US 2011/0061721 describes a non-imaging lens with a Fresnel type of structure, that is a structure with triangles with a given distribution of angles.
US 2004/0141323 describes an indicator lamp comprising a light source and a coaxial annular reflector with a structured inner surface.